Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session T2: Surfaces, Nanoparticles, and Materials |
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Sponsoring Units: DCP Chair: Gilbert Nathanson, University of Wisconsin-Madison Room: 102 |
Thursday, March 6, 2014 11:15AM - 11:27AM |
T2.00001: Galactose adsorption on Ru(0001) Matti Alatalo, Mikko Puisto In order to understand the valorisation of biomass, it is essential to study the behavior of sugar molecules on catalytic surfaces. We have studied the adsorption of galactose molecules on the Ru(0001) surface using first principles calculations. We present results for the fully relaxed configurations of the molecule at different adsorption sites. We also compare the effect of the inclusion of the van der Waals interactions on both the energetics of the free galactose molecule and the adsorption energy of galactose on Ru(0001). We compare our results, obtained using periodically repeated supercells, to those obtained with cluster calculations. [Preview Abstract] |
Thursday, March 6, 2014 11:27AM - 11:39AM |
T2.00002: Surface-Specific Hubbard $U$ calculations for $\alpha$-Fe$_2$O$_3$ (0001) Surfaces Xu Huang, Sai Kumar Ramadugu, Sara Mason The (0001) surface of $\alpha$-Fe$_2$O$_3$ exists in different terminations that exhibit chemically distinct Fe atoms. The widely studied terminations for this plane are: -O3Fe, -O3Fe2, the ferryl termination (-Fe=O), -Fe2O3, and -Fe3O3. Using GGA+$U$ on the above surface terminations, it has been shown that the most stable terminations in the high oxygen chemical potential were -O3Fe and -Fe=O whereas in the standard GGA the most stable terminations were shown to be -Fe2O3 and -Fe3O3. Experimental studies have shown that the results from standard GGA are in better agreement with the experimental phase diagram. It is known that reducing the dimensionality of bulk hematite to form surfaces results in Fe surface sites that are not chemically equivalent to bulk Fe, and this is proposed to be problematic for DFT+$U$ approaches that apply the same $U$ value throughout to all Fe atoms in the slab. In the current work we show that the surface-specific derived Hubbard $U$ values from the response matrix method affects the energetics, electronic structure, and relative stabilities of $\alpha$-Fe$_2$O$_3$ (0001) surface structure. [Preview Abstract] |
Thursday, March 6, 2014 11:39AM - 11:51AM |
T2.00003: Synthesis and Cs-Corrected Scanning Transmission Electron Microscopy Characterization of Multimetallic Nanoparticles Subarna Khanal, Nabraj Bhattarai, Jesus Vel\'azquez-Salazar, Miguel Jose-Yacaman Multimetallic nanoparticles have been attracted greater attention both in materials science and nanotechnology due to its unique electronic, optical, biological, and catalytic properties lead by physiochemical interactions among different atoms and phases. The distinct features of multimetallic nanoparticles enhanced synergetic properties, large surface to volume ratio and quantum size effects ultimately lead to novel and wide range of possibilities for different applications than monometallic counterparts. For instance, PtPd, Pt/Cu, Au-Au$_{3}$Cu, AgPd/Pt, AuCu/Pt and many other multimetallic nanoparticles have raised interest for their various applications in fuel cells, ethanol and methanol oxidation reactions, hydrogen storage, and so on. The nanostructures were analyzed by transmission electron microscopy (TEM) and by aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM), in combination with high angle annular dark field (HAADF), bright field (BF), energy dispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) detectors. These techniques allowed us to probe the structure at the atomic level of the nanoparticles revealing new structural information and elemental composition of the nanoparticles. [Preview Abstract] |
Thursday, March 6, 2014 11:51AM - 12:03PM |
T2.00004: Computational Design of Bimetallic (Au-Cu {\&} Ag-Cu) Catalyst for Low Temperature CO Oxidation Altaf Karim, Abdul Rauf, Akhtar Hussain Au--Cu and Ag-Cu bimetallic surfaces are reported to be much more active in CO oxidation than the mono-metallic Pt, Cu, Au, {\&} Ag in our work. First, we used theoretical and experimental results of CO oxidation~on Pt surfaces to benchmark and optimize our multiscale modeling framework. Further, we extended this~framework to examine the molecular oxygen adsorption,~decomposition, and CO oxidation upon a number of Cu modified Au surfaces~cleavaged~in (100) orientation. The~amount of Cu was varied on the Au slab to optimize the model that serves as the best one to investigate the synergic effect between Au and Cu for CO oxidation process.~Comparison between different surfaces suggests that the Cu-modified Au surface is superior and more active than pure Cu toward CO oxidation. Similarly, a slab of Ag--Cu having a top monolayer of Cu and three layers beneath is also equally active as Au-Cu. Computational and experimental results show that these surfaces are good candidates for low-temperature CO oxidation.~ [Preview Abstract] |
Thursday, March 6, 2014 12:03PM - 12:15PM |
T2.00005: The Adsorption of Polyatomic Molecules on Carbon Surfaces Jared Burde, Mercedes Calbi We study the adsorption of hydrocarbon chains on several carbon surfaces. We focus on the kinetics of adsorption, working to elucidate the factors that have the greatest influence on the time needed for the system to reach equilibrium. Preliminary results suggest that a major factor is the effective energy, which includes the binding energy, interaction energy with neighboring adsorbates, and other system parameters. We use computational and analytical techniques to determine the relationship between the adsorption rate and effective energy of several hydrocarbon chains (including methane, ethane, and propane) as they condense on carbon substrates (like graphene and carbon nanotubes). [Preview Abstract] |
Thursday, March 6, 2014 12:15PM - 12:27PM |
T2.00006: A concentration dependence of the low temperature fluorescence of Neodymium (III) doped Gadolinium Gallium Garnet Christopher Ferri, Jacky Wan, Michael Tennenbaum, Sayantani Ghosh We perform temperature and concentration dependent studies on the $^{4}F_{3/2} \to ^{4}I_{9/2}$ transition of Neodymium dopant in Gadolinium Gallium Garnet. Optical spectra are taken at a range of temperatures between 5K and 300K for all three concentrations: 0.1 at.\%, 0.5 at.\% and 1 at.\%. The transitions centered at 11000 $cm^{-1} (R_{n} \to Z_{5})$ are fit with Voigt profiles. Subsequently, we analyze each of the profile parameters as a function of temperature. We find that the linewidth of the dominant transition $(R_{1} \to Z_{5})$ experiences broadening below 50K that can not be explained using phonon-ion theory. We posit this low temperature broadening is due to the approaching paramagnetic to spin liquid phase transition. We also find that the inhomogeneous broadening of all of the transitions has a temperature dependence suggesting that thermal expansion of the crystal is an important effect, but the energy shifts of the transitions are adequately explained without including a crystal expansion term in the analysis. [Preview Abstract] |
Thursday, March 6, 2014 12:27PM - 12:39PM |
T2.00007: Thermoelectric Transport Properties of Hypothetical Type-VIII Clathrate Si$_{46}$ Payam Norouzzadeh, Charles Myles, Daryoosh Vashaee Our first principles calculations on hypothetical type-VIII clathrate Si$_{46}$ [1] revealed that it has a large density of states near the band edges which can result in large thermoelectric power factor. The large number of valleys around the valance band edge can improve the performance of p-type thermoelectric material. The calculated thermoelectric transport properties using~multiband Boltzmann transport equation and the data from density functional theory and molecular dynamics simulations~are presented for the bulk crystalline and the effect of nanostructuring is investigated as well. The predicted figure-of-merit of bulk nanostructured p-type Si$_{46}$-VIII clathrate is in the order of 2 at 1000 C. The InfraRed and Raman active modes are identified~which will be especially useful for the experimental characterizations of this material.\\[4pt] [1] Payam Norouzzadeh \textit{et al} 2013 \textit{J. Phys.: Condens. Matter} \textbf{25} 475502 [Preview Abstract] |
Thursday, March 6, 2014 12:39PM - 12:51PM |
T2.00008: Single crystal synthesis and magnetism of the BaLn$_{2}$O$_{4}$ family (Ln$=$lanthanide) Tiglet Besara, Jeffrey Whalen, Matthew Lundberg, Daniel Ramirez, Jifeng Sun, Lianyang Dong, Theo Siegrist The BaLn$_{2}$O$_{4}$ family (Ln$=$La-Nd, Sm, Gd-Yb) has been synthesized for the first time in single crystalline form using a novel metal flux method. The family crystallizes in the CaV$_{2}$O$_{4}$ structure with quasi-one-dimensional zigzag chains of lanthanides, and we present a study of the structure details as the lanthanide goes from La to Yb. Magnetic susceptibility measurements on the series reveal that, while one analog (Gd) orders at low temperatures, some of the others (Tb, Ho, Nd) display magnetic anomalies. Some of the analogs (Ce, Tb, Nd, Yb) exhibit a susceptibility that clearly deviates from the Curie-Weiss behavior, due to crystal field effects. In general, the series display geometrically frustrated antiferromagnetic interactions. [Preview Abstract] |
Thursday, March 6, 2014 12:51PM - 1:03PM |
T2.00009: Ultrafast Optical Studies of Carrier Relaxation Dynamics in PbSe Nanoplatelets Andrew Fidler, Weon-Kyu Koh, Claudiu Cirloganu, Nikolay Makarov, Istvan Robel, Victor Klimov Two-dimensional materials have attracted widespread interest due to their unique electrical, optical, and mechanical properties. Most of the two-dimensional materials currently available have a layered crystal structure, allowing for the efficient mechanical cleavage of bulk materials to isolate individual monolayers. The synthesis of new classes of two-dimensional materials with non-layered crystal structures remains challenging. Here we present optical studies of an emerging class of two dimensional materials, a colloidal suspension of thin lead selenide nanoplalets. Due to the large Bohr radius of lead selenide ($\sim$ 46 nm), our nanoplatles of size 30 x 30 x 2 nm exhibit the effects of quantum confinement in all three dimensions. Using transient absorption and time resolved photoluminescence measurements we characterize the dominant relaxation pathways to explore how asymmetric confinement influences the carrier dynamics. Potential applications of lead selenide nanostructures arising from their small bandgap, such as infrared detectors as well as photovolatics are discussed. [Preview Abstract] |
Thursday, March 6, 2014 1:03PM - 1:15PM |
T2.00010: Single Molecule Approaches for Two Dimensional Nanostructures Thomas Baker, Shajun Guo, Weon-Kyu Koh, Nikolay Makarov, Andrew Fiddler, Istvan Robel, Victor Klimov A variety of two dimensional semiconductor nanostructures have been synthesized recently by a number of different groups. Of these, nanoplatelets made of a single to few layers of material have shown interesting promise due to confinement in only a single direction. The photophysics of these types of structures show large exciton binding energies and narrow emission widths in ensemble measurements. Only a few single molecule experiments have been reported in the literature and we hope to expand the insights that single molecule techniques can provide in the understanding of these new materials. Our group has recently extended our synthetic expertise gained from quantum dots into these 2D nanoplatelets including CdSe, MoS$_{\mathrm{2}}$ and graphene. Time correlated single photon counting experiments at the single molecule level provide information on the homogenous linewidths, quantum yield variations, and fluorescence lifetimes. Furthermore, two photon correlations at zero time delay allow us to confirm the single molecule nature of the emission and potentially determine biexciton quantum yields and lifetimes. [Preview Abstract] |
Thursday, March 6, 2014 1:15PM - 1:27PM |
T2.00011: Phase diagram and Equation of State of Boron Carbide Tadashi Ogitsu, Sebastien Hamel, Andrew Shamp, Eva Zurek Boron carbide is considered to be a good candidate material as ablator for inertial confinement fusion yet its phase diagram and equation of state are not well established. In the talk, we will first briefly summarize our current understanding of the phase diagram of boron carbide and the some of the important aspects such as uncertainty in the stoichiometry of real sample, which affects on the phase stabilities of boron carbide. We will then discuss about the progresses on the understanding of high-pressure phases of boron carbide predicted by the ab-initio crystal structure prediction method. [1] This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [1] D. C. Lonie, E. Zurek, Computer Physics Communications 182, 372 (2011). [Preview Abstract] |
Thursday, March 6, 2014 1:27PM - 1:39PM |
T2.00012: Formation, stability, and reactivity studies of neutral iron sulfide clusters Shi Yin, Zhechen Wang, Elliot Bernstein Different methods are used to generate neutral iron sulfide clusters to study their formation, stability, and reactivity, employing a time of flight mass spectrometer (TOFMS) with VUV (118 nm) radiation single photon ionization (SPI). Neutral Fe$_{m}$S$_{n}$ ($m \quad =$ 1-4, $n \quad =$1-6 ), and hydrogen containing Fe$_{m}$S$_{n}$H$_{x}$ ($x$ \textgreater 0,$ n$ \textgreater $m)$ clusters are generated by the reaction of seeded H$_{\mathrm{2}}$S in a helium carrier gas with laser ablated iron metal within a supersonic nozzle. The observed strong signal of association products Fe$_{\mathrm{2}}$S$_{\mathrm{2}}$(SH)$_{\mathrm{0,1}}M$ ($M \quad =$ CO, C$_{\mathrm{2}}$H$_{\mathrm{4}}$, C$_{\mathrm{3}}$H$_{\mathrm{6}})$ suggest that the Fe$_{\mathrm{2}}$S$_{\mathrm{2}}$(SH)$_{\mathrm{0,1}}$ clusters have the high activity for interactions with these small molecules. In order to avoid the effect for reactivity from hydrogen containing clusters, pure Fe$_{m}$S$_{n} $clusters are generated through laser ablation of a mixed iron/sulfur target in the presence of a pure helium carrier gas. (FeS)$_{m}$ ($m \quad =$ 1-4) is observed to be the most stable series. Reaction of CO and H$_{\mathrm{2}}$ on neutral (FeS)$_{\mathrm{1,2}} $clusters is farther investigated both experimentally and theoretically. A size dependent reactivity of iron sulfide clusters \quad toward CO is characterized. The reaction FeS $+$ CO $\to $ Fe $+$ OCS is found for the FeS cluster. Products Fe$_{\mathrm{2}}$S$_{\mathrm{2}}^{\mathrm{13}}$COH$_{\mathrm{2}}$ and Fe$_{\mathrm{2}}$S$_{\mathrm{2}}^{\mathrm{13}}$COH$_{\mathrm{4}}$ are identified for reactions of $^{\mathrm{13}}$CO and H$_{\mathrm{2}}$ on Fe$_{\mathrm{2}}$S$_{\mathrm{2}}$ clusters: this suggests that the Fe$_{\mathrm{2}}$S$_{\mathrm{2}}$ cluster has a high catalytic activity for hydrogenation reactions of CO to form formaldehyde and methanol. DFT calculations are performed to explore the potential energy surfaces for the two reactions: Fe$_{\mathrm{2}}$S$_{\mathrm{2}} \quad +$ CO $+$ 2H$_{\mathrm{2}} \quad \to $ Fe$_{\mathrm{2}}$S$_{\mathrm{2}} \quad +$ CH$_{\mathrm{3}}$OH; and Fe$_{\mathrm{2}}$S$_{\mathrm{2}} \quad +$ CO $+$ H$_{\mathrm{2}} \quad \to $ Fe$_{\mathrm{2}}$S$_{\mathrm{2}} \quad +$ CH$_{\mathrm{2}}$O. [Preview Abstract] |
Thursday, March 6, 2014 1:39PM - 1:51PM |
T2.00013: The role of ligands effect in the atomic and electronic structure of Pt$_{55}$ and Au$_{55}$ nanoclusters Diego Guedes Sobrino, Maur\'Icio J. Piotrowski, Juarez L.F. Da Silva One of the greatest problems in the use of transition-metal nanoclusters in nanocatalysis is the environment effects induced by ligands, which affects the atomic and electronic properties, and hence, their reactivity, however, our atomistic understanding is far from satisfactory due to complex nature of the ligand-metal interactions. In this talk, we will report a first-principles investigation of ligand effects (PH$_3$, SH$_2$) on the physical and chemical properties of Pt$_{55}$ and Au$_{55}$ using density functional theory (FHI-aims). We found that a reduced core structure ($7 - 10$, instead of 13), called LOW, is about 5.45~eV (2.00~eV) lower in energy than the icosahedron (ICO) model for Pt$_{55}$ (Au$_{55}$) ($\Delta E_{\rm tot} = E_{\rm tot}^{\rm LOW} - E_{\rm tot}^{\rm ICO}$), which is consistent with previous results. Furthermore, spin-orbit coupling does not affect the relative stability. We found that the addition of ligands, from 1 to 18, decreases $\Delta E_{\rm tot}$ to about $-0.25$ (Pt$_{55}$) and 0.07~eV (Au$_{55}$) for 18 PH$_3$ ligands, and $-0.10$ (Pt$_{55}$) and 0.17~eV (Au$_{55}$) for SH$_2$ ligands. We observed an average increase of about 0.70\% in the bond lengths due to the ligand effects, however, it affects only slightly the coordination number. [Preview Abstract] |
Thursday, March 6, 2014 1:51PM - 2:03PM |
T2.00014: Assembling Ge$_6$Au$_N$ Structures From Ge$_6$ Building Blocks Kathie Newman, Danielle McDermott Unusual crystalline germanium materials useful for optical and semiconducting devices can been synthesized through precursors of small anionic Ge clusters. Furthermore, a successful catalyst of germanium nanowires are gold nanoparticles, yet theoretical methods to describe the Au-Ge interaction are incomplete. Thus we apply Density Functional theory to a series of neutral and anionic Ge$_6$ clusters linked with gold atoms to form Ge$_{12}$Au$_N$ molecules where N = 0,1,2,3. We present the lowest energy Conjugant Gradient relaxed clusters and perform short Molecular Dynamics simulations to evaluate their stability. The gold-germanium bondlengths and angles affect the electronic properties of the molecules, which we characterize with total and partial Density of States and the COHP (Crystalline Orbital Hamiltonian Population) method. The electronic structure reveals a stability motif in which gold donates stabilizing electrons. This suggests how Ge$_6$ can form extended structures of Ge$_6$Au$_N$ such as 1D chains and 2D surfaces. [Preview Abstract] |
Thursday, March 6, 2014 2:03PM - 2:15PM |
T2.00015: Characterization of the Surface of Colloidal Ag NPs by Second Harmonic Light Scattering Grazia Gonella, Bolei Xu, Brendan G. DeLacy, Hai-Lung Dai Noble metal nanoparticles (NPs) have been studied extensively for their unique optical properties. These properties stem from the fact that metallic NPs can sustain localized surface plasmons (LSPs). We have used second harmonic light scattering (SHS), a coherent and surface-specific technique, to probe citrate-stabilized colloidal Ag NPs and proven that, by using a fundamental beam at twice the wavelength of the LSP resonance, the detected SH signal is generated predominantly at the Ag NP surface. We have also determined how the composition, shape and second-order susceptibility affect the SHS signal from the Ag NPs. Very recently, as self-assembled monolayers (SAMs) on metallic NPs have been rediscovered for their potential in catalysis and as biosensors among others, we have used SHS to study the adsorption process of thiol molecules on the surface of Ag NPs exploiting the ability of non-SH-active thiols to quench the SH signal from the Ag NP surface. [Preview Abstract] |
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